The present invention relates to lenticular parallax panoramagrams, and more particularly to a variable aspect display capable of providing significant visual information which changes according to predetermined conditions. The changes occur in most cases without requiring any internal energy within the display, thereby making it useful for many specialized as well as conventional applications.
Lenticular paralax panoramagrams have been known for over a half-century, and precursors operating on similar principles extend back yet another quarter century. Although these and other prior art devices have suggested diverse applications for lenticular parallax panoramagrams, and although the literature shows multi-lens structures conceptually similar to lenticular parallax panoramagrams, their commercial use has been limited almost exclusively to novelty items. For more serious applications, such displays must provide performance and reliability features generally lacking in known lenticular parallax panoramagram configurations.
In the broadest sense, such a panoramagram may be defined as a patterned field which is set at or near the foci of a group of lenses so that a viewer at a considerable distance sees only the parts of the field that are substantially at conjugate focal positions with respect to his eyes. Known prior art configurations meet this definition, but as indicated, their use in more sophisticated applications, such as traffic control and/or warning signs, is not presently being realized.
The traffic sign provides a good example of both the great advantages which are possible with a variable aspect display, and the considerable practical difficulties associated therewith which, in large measure, may account for the lack of satisfactory designs beyond that of the novelty type. Of the advantages, perhaps most noteworthy is the ability of such a sign to capture the viewer's attention. Consider the effect, for example, of travelling along a darkened rural highway at night, with a yellow sign ahead warning of a curve. If, upon nearing the sign, it suddenly started "flashing" at the driver, either alternately appearing and disappearing, alternating its colors (e.g., yellow, black, yellow, etc.), or changing its message altogether, the effect upon the driver's attention would be remarkable.
Other examples can include an arrow which alternately extends and retracts, a "progressive" message which advances through several stages (either textual or graphic), as well as many other varieties. As taught later herein, the rate at which the display changes can also be varied according to conditions. Ideally, such a sign would require no artificial illumination during the day or night. Nighttime illumination would be provided by the automobile headlights, so that no internal energy source would be required. As it is, however, the prior art has failed to provide such a sign.
In looking for the reasons for this failure, consider first that a traffic sign must be clear and unambiguous. This means that the display which is presented must at all times be a precise function of the positional relationships between the viewer and the sign, and must preferably be capable of being tailored to each particular anticipated viewing position. This is a virtual impossibility where the lens elements share display elements with adjacent lenses, a dominant feature of conventional lenticular parallax panoramagram constructions. Further, the circular aberration of simple, inexpensive lenses at off-center viewing angles may not provide sufficient distinctness and sharpness for such applications.
An even greater limitation, as explained further hereinbelow, may render such a sign all but useless at night. Typically, the source of illumination at night would be the automobile headlights, and the lens system will focus the light from the headlights upon corresponding conjugate portions of the object field. The light reflected therefrom will then be focused and returned by the lenses, not to the driver, but to the headlights. Thus the conjugate portions of the object field corresponding to the angular positions of the headlights will be illuminated, but those corresponding to the angular positions of the driver's eyes typically will not.
The significance of this condition, of course, varies as a function of the relative angles, distances, and quality of the optics, and may not be significant at great viewing distances. However, as the viewer approaches the sign, the problem would be increasingly aggravated. In fact, experiments have shown that even when inexpensive, optically inferior commercially available fluted glass is used for lens elements, angular deviations between the headlights and the driver's eyes of less than one degree will cause the sign to appear dark at night when illuminated by the headlights.
Still other problems of a practical nature must be considered. Signs of a considerable width as seen from the viewer's position may require correction for parallax. Signs which are exposed to daily and seasonal temperature variations may suffer from differential rates of thermal expansion and contraction between the lenticular lens screen and the object field, causing relative displacement and misalignment of lens and field elements, and obscuring the display.
A need thus remains for a variable aspect display which provides the substantial advantages potentially available with a lenticular parallax panoramagram, but which overcomes its disadvantages. Such a variable aspect display should lend itself to use in the widest variety of applications. It should be durable and reliable, yet inexpensive and readily suited to convenient mass production.